1. Field of the Invention
The present invention relates to an apparatus for fabricating an electroluminescent display device, particularly to an apparatus for fabricating an electroluminescent display device capable of distributing a stress applied to a mask uniformly to form a precise and reliable pixel.
2. Description of the Related Art
Recently, various kinds of flat display devices having less weight and volume have been developed to substitute the cathode ray tube (CRT) having huge weight volume. Liquid crystal display device, field emission display device, plasma display panel and electro-luminescence display device (hereinafter, referred to as “EL” display device) are the examples of such flat display devices.
Among these flat display devices, the EL display device is a self-light emitting device in which light is emitted from fluorescent material by re-combining holes with electrons. The EL display device is classified into non-organic EL display device using nor-organic material as fluorescent material and organic EL display device using organic material as fluorescent material.
Compared with a passive light emitting device requiring additional light source such as liquid crystal display device, the EL display device is advantageous in that the response time is short to the same level as the cathode ray tube. Also, the EL display device has many advantages such as low-voltage drive, self-light emission, thin film shape, wide view angle, short response time, high contrast and the like, and so is expected to be the next generation display device.
FIG. 1 is a sectional view showing the structure of general organic EL cell for illustrating a light-emitting principle of organic EL display device. The organic EL cell comprises an organic light-emitting layer 110 disposed between an anode 104 and a cathode 112, the organic light emitting layer 110 consists of an electron injection layer 10a, an electron transport layer 10b, an light emitting layer 10c, a hole transport layer 10d and a hole injection layer 10e. 
Once power voltage is applied to the anode 104 and the cathode 112, electrons generated from the cathode 112 are transported toward the light emitting layer 10c through the electron injection layer 10a and the electron transport layer 10b. Also, holes generated from the anode 104 are transported toward the light emitting layer 10c through the hole injection layer 10e and the hole transport layer 10d. Accordingly, electrons supplied through the electron transport layer 10b are collided and re-combined with holes supplied through the hole transport layer 10d in the light emitting layer 10c, and so and the light is emitted. This light is radiated to an exterior through the anode 104 to display an image.
FIG. 2 is a view showing the organic EL display device.
In the organic EL display device shown in FIG. 2, first electrodes 104 (hereinafter, referred to as “anodes”) and second electrodes 112 (hereinafter, referred to as “cathodes”) are formed on a substrate 102 in a crossing direction each other.
The anodes 104 are formed on the substrate 102 by certain distance from each other. On the substrate 102 on which the anodes 104 are formed, an insulating layer (not shown) having a plurality of openings is formed, wherein each opening corresponds to an EL cell area. Walls 108 are formed on the insulating layer to divide the organic light emitting layers 110 and the cathodes 112 formed thereon. Each wall 108 is formed in the direction perpendicular to the anodes 104, and has an inverse taper structure in which the upper end side is larger than the lower end side.
After the walls 108 are formed on the insulating layer, the organic light emitting layers 110 made of organic material and the cathodes 112 are sequentially formed on the entire insulating layer. As shown in FIG. 1, the hole injection layer 10c, the hole transport layer 10d, the light emitting layer 10c, the electron transport layer 10b and the electron injection layer 10a are sequentially formed to form each organic light emitting layer 110.
Here, red (R) colored light-emitting layer, green (G) colored light-emitting layer and blue (B) colored light-emitting layer are formed on the EL cell areas by using a stretched mask provided in the manufacturing apparatus.
The light emitting layer 10c of the organic EL display device shown in FIG. 1 is formed through thermal deposition and vacuum deposition processes using a grill mask. The grill mask has a plurality of grills formed thereon and corresponding to the light emitting layers to be formed on the substrate. The manufactured grill mask is stretched by a mask clamping/stretching apparatus into a predetermined dimension, and then fixed to a mask frame of the manufacturing apparatus.
In the process for forming the light emitting layer, the mask fixed to the mask frame is placed on a surface of the substrate, and so the light emitting layer 10c is formed on a surface of the substrate corresponding to the grill formed on the mask.
A plurality of grippers are mounted to the mask clamping/stretching apparatus. By pulling the grippers in the state that mask is gripped with the grippers, the mask is stretched. In this process, a stress is applied onto portions corresponding to each gripper in a periphery of the mask. If the magnitude of stress applied to one portion of the mask differs from that applied to another portion for some reasons, the magnitude of tension force applied to one grill differs from that applied to other grills depending on a position of the grill. As a result, the stretching amounts of the grills cannot but differ from each other.
If the stretching amounts of the grills differ from each other, sizes (areas) of the light emitting layers formed by the grills of the mask also become different from each other. Accordingly, each light emitting layer is not formed correctly on the predetermined position, and sizes (areas) of the light emitting layers in the display device are different from each other.